1. Field of the Invention
The invention concerns a cosmetic composition wherein ceramides are stably incorporated into a nonseparating product.
2. The Related Art
Ceramides are an important group of lipids, members of which are found in the epidermis of mammals. Skin ceramides are believed to play an important role in the water permeability properties of the skin, providing an epidermal water-barrier which functions to give increased strength to the skin structure and to decrease water loss and so improve the condition of the skin.
Ceramides are N-acylated sphingosine bases. Sphingosine bases are of variable chain length and have the general formula (1): EQU CH.sub.3 (CH.sub.2).sub.x ACHOHCH(NH.sub.2)CH.sub.2 OH (1)
where A is --CH.dbd.CH-- (sphingosine), --CH.sub.2 CHOH-- (phytosphingosine) or --CH.sub.2 CH.sub.2 --(dihydrosphingosine), and where x is generally in the broad range 7 to 27, more typically in the range 10 to 16. It should be noted that sphingosines contain asymmetric carbon atoms and so various stereoisomers are possible. Sphingosine/ceramides from especially mammalian sources are all the D-erythro isomer and phytosphingosine/phytoceramides the D-D-erythro isomer. Seven distinguishable groups of ceramides have been identified in pig and human epidermis. Each group consists of molecules of varying fatty acid chain length. The structures of typical skin ceramides are described in the paper entitled "Ceramides of Pig Epidermis: Structure Determination" by P. W. Wertz and T. T. Downing in Journal of Lipid Research, Col. 24, 1983, pages 759-765.
Problems have been encountered when phytosphingosine-containing ceramides are incorporated into pharmaceutically acceptable carrier systems. These ceramides are extremely insoluble, especially in ester type carriers and where single phase transparent formulas are sought.
Accordingly, it is an object of the present invention to provide a phytosphingosine-containing ceramide composition wherein all components including the ceramide are dissolved or at least stably suspended. Another object of the present invention is to provide a phytosphingosine-containing ceramide cosmetic composition which is a clear (transparent) formula.
These and other objects of the present invention will become more apparent from consideration of the following summary and detailed description.